1. Field of the Invention
The present invention relates to a communication system using a frequency overlay scheme. More particularly, the present invention relates to an apparatus and method for transmitting/receiving a paging message in a frequency overlay communication system.
2. Description of the Related Art
As communication systems are evolving, the services they provide are expanding and diversifying. For example, while previous communication systems provided only voice communication between users, current communication systems provide additional services such as video communication, digital broadcasting, Internet communication, and the like. To support these advanced features and services, additional bandwidth is necessary to provide the additional information. Accordingly, research and development in the field of broadband communication is very active.
To support broadband communication, at least two issues must be considered. First, frequency resources for any communication system are limited. That is, only a limited number of frequencies are available for a given system. Accordingly, as communication technology is developed, demand for the use of a frequency band increases, especially for frequency bands supporting broadband service. Thus, a license cost for the frequency band use increases. Second, compatibility with existing systems must be considered. That is, a new broadband communication system must be implemented with consideration of user equipment that was designed for an older system. Because both the limited frequency resources and the backward compatibility with previously installed communication systems must be considered, design of a broadband communication system can be difficult. Moreover, due to the increase in the license cost for the frequency band and the difficulty in backward compatibility, various schemes that are proposed to provide a broadband service may be delayed and potentially not implemented at all.
To address the consequences of the limited frequency bands, that is, to address the problem of the increased license costs and to smoothly provide the new broadband services without interruption to existing services, various schemes have been proposed. In one such scheme, a frequency overlay system is proposed. A frequency overlay system is a system in which some or all frequency bands of an advanced broadband communication system are overlapped with some or all frequency bands of legacy communication system. That is, both the new broadband communication system and the existing legacy communication system use at least one common frequency band. For example, a Code Division Multiple Access 2000 3x (CDMA2000 3x) communication system, an overlay Orthogonal Frequency Division Multiplexing (OFDM) communication system, etc. may be considered. In such a case, a Mobile Station (MS) designed for use in the broadband communication system and an MS designed for use in the legacy communication system can either exist together in the legacy communication system or can exist together in the broadband communication system.
In a frequency overlay system, a Base Station (BS) providing service to an MS periodically transmits a paging message to the MS. The paging message is used to instruct the MS, which is in an idle state, to update its position information or initialize service with the BS. Thus, the MS in the idle state periodically wakes up, receives the paging message, and performs the received instruction. More specifically, if a BS detects that traffic exists which needs to be sent to the MS, the BS sends a paging message to the MS indicating that traffic exists for the MS. Periodically, the MS wakes up to detect whether the paging message exists and, if it does exist, receives the paging message.
In a frequency overlay system, when a legacy MS connects to an advanced BS, the legacy MS may utilize any frequency band of the advanced BS. In such a situation, if the BS detects that traffic exists which needs to be sent to the MS, the advanced BS sends a paging message to the MS through all frequency bands used by the advanced BS. In this case, by sending the paging message over all frequency bands used by the advanced BS, the frequency bands are inefficiently used since the MS needs to receive the paging message on only a single frequency band. Because the frequency bands of an advanced system have high costs, their inefficient use causes great concern.
To address the frequency band inefficiency problem, the advanced BS can allocate a specific frequency band for sending paging messages. However, when a plurality of paging messages for different MSs are sent through the specific frequency band, it causes a problem of collision among the paging messages.
Accordingly, there is a need for an apparatus and method for efficiently transmitting a paging message to an MS of a broadband communication system and an MS of a legacy communication system by a BS of a broadband communication system forming a communication channel with each MS.